Is it possible to define a public variable of type UnityEngine.Object?

I was wondering if it is possible to create a public variable of type UnityEngine.Object.

I am trying to create a class that has a public variable where I can assign a video file(mp4) by dragging and dropping the file into the variable slot in editor. I then get the name of the Object and then use the name to play the video using a video playing asset.

This seems to work fine in the editor but when I build the project, the UnityEngine.Object that is received as a public variable is always null.

Any ideas why?